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Old 02-23-2009, 04:25 PM   #1
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Dual exhaust question

I have an oppurtunity to get a cat back dual exhaust installed on my mini-van (waiting for the laughter to subside) for $90. How much power/fuel economy can I gain from this?
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Old 02-23-2009, 05:07 PM   #2
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Probably none. Consider these points...
  • The minivan comes from the factory with a system designed by expert engineers under pressure from CAFE and from a marketing department that wants to deliver extra power due to the stodgy image of minivans.
  • There are few design compromises necessary these days; OEM mufflers are quiet, free-flowing, and no more expensive for the manufacturer than they should be.
  • The OEM system is designed to handle the full amount of airflow that the engine can make at its maximum power -- WOT@redline.
  • As someone interested in saving gas, you're probably never going anywhere NEAR that amount of flow.
Now, that said...if it's good quality stainless steel and will last as long as the rest of the minivan, as the OEM system likely would, then it's still a nice upgrade for a measly $90. If it were me I'd probably go for it and just not expect any real improvement.

An upgraded exhaust system is important when upgrading other stuff too. For it to help power, I'd expect you would also need to upgrade most of the intake system and the ECU at the least.
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Old 02-24-2009, 06:26 AM   #3
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There are two rather major flaws in all of that logic....

One of the biggest focuses of OEM exhaust/intake systems is quietness, and cheapness. If the pipes are anything but mandrel bent (Only now done on hi-po cars) they're restricting at WOT. And if it's so quiet you can't hear it running... It's restricting.

There's also the fact that minivans are never sold based on horsepower, they're sold based on convenience and comfort. And part of comfort is quiet. There is no incentive to eke every last horsepower out of the engine that they can, so they don't spend nearly as much time perfecting the exhaust as they would in an SRT car or something like that.



Your statements are true, to a limit, when dealing with modern High Performance cars, as they do want to squeeze every horsepower within reason out of their cars. However, still... They need to make them reasonably quiet and keep production costs down. Which is why exhaust upgrades are a reliable way to increase power with almost every car. With an '05 Mustang GT, a magnaflow cat-back system was dyno proven to gain 11hp. Worth the high cost of such a system? Doubtful. But showing actual gains? Yup. Definately.


Basically, in every car, if there was at all a desire to keep either sound or cost down, you can improve the intake and exhaust for power, over OEM. The less of a desire there was to keep sound and cost down... The less you'll gain.
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Old 02-24-2009, 10:29 AM   #4
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I'd be worried that the new, cheap catback exhaust would rust out quicker than the stock exhaust. Is it stainless steel?
You might gain 5hp, which is barely noticeable. I'd be suprised if you saw any gains in FE. OTOH there's a good chance the new catback is noisier. Quality exhausts will cost more than $90.
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Old 02-24-2009, 12:25 PM   #5
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my only thought was that you MIGHT realize FE gains IF your present exhaust was old/leaking. but, i see your van is a 2007, so it's doubtful based on that premise.
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Old 02-24-2009, 01:00 PM   #6
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What are your exhaust manifolds like? Log style or the more conventional extractor type?
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Old 02-24-2009, 03:50 PM   #7
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The retail on the exhaust is $250 but my discount would be 60%. I have no idea what my exhaust manifolds are like. I just think it would be funny to have dual exhaust on a mini-van but I think my wife is going to veto the move based on the "that's a stupid waste of $90" arguement.
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Old 02-24-2009, 04:00 PM   #8
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Quote:
Originally Posted by Greyg View Post
I think my wife is going to veto the move based on the "that's a stupid waste of $90" arguement.
There is no lack of stupid wastes of money on a car to be seen on the road. If you want to counter that one go show her a van with spinners or something.
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Old 02-25-2009, 04:22 AM   #9
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The deal about bigger exhausts has to do with exhaust gas velocity and the engine's powerband. Bigger pipes allow a higher CFM flow at a lower velocity, smaller pipes allow a smaller CFM flow at a higher velocity. The bigger pipes generally move the powerband of the engine up higher, and the smaller ones down lower.

I really wouldn't reccomend duals. If you're going to do this and they do not have mandrel bent piping (95%+ of shops only do crush bent), 1/4" to 1/2" bigger DIA than the SMALLEST dia on the stock system should treat you pretty good as a rule of thumb.

I've got a 2.25" mandrel bent straight through exhaust system on the Saturn. I'm getting improvements in gas milage because the cat was bad, but it's a pretty fair amount of a gain. I also put on a ceramic coated header, which has a lot to do with it. When my car's not having problems with other things breaking, I'm using 2-5% less throttle on the highway. I used to need about 15-16% throttle to cruise behind a truck at 55MPH - now it's 10-12%. The highway economy has gone way up, but the city hasn't really moved too much.
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Old 02-25-2009, 04:22 PM   #10
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Quote:
Originally Posted by Greyg View Post
The retail on the exhaust is $250 but my discount would be 60%. I have no idea what my exhaust manifolds are like. I just think it would be funny to have dual exhaust on a mini-van but I think my wife is going to veto the move based on the "that's a stupid waste of $90" arguement.
You have a 2007 T&C......those are really awesome for a minivan. There is 07 T&C in the family. You can watch movies and play cards on a table in the back and tons of storage space. Keeps the kids occupied. Never drove it but rode in it once. Very comphy seats and a very smoothe ride.

Anyway, you probably already have stainless steel exhaust. Personally I do not think you will gain anything though. You will just be out the money spent, so I guess I will have to agree with your wife on this one........ Sorry.

Just my opinion.
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